Circuit breakers



Sept. 27, 1955 WITNESSES:

F. L. GELZHEISER ET AL CIRCUIT BREAKERS Filed May 2, 1952 INVENTORSStephen S. Dobrosielski.

Francis L. Gelzheiser 8 United States Patent crncurr BREAKERS Francis L.Gelzheiser, Pittsburgh, and Stephen 5. Dohrosielski, Beaver, Pa.,assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application May 2, 1952, Serial No. 285,696

13 Claims. (Cl. 2062-144) This invention relates to circuit interruptersand, more particularly, to are extinguishers and venting arrangementsfor facilitating the rupture of arcs drawn between the cooperatingcontacts and the expulsion of the hot arc gases from such circuitinterrupters.

An object of the invention is to provide a circuit breaker with animproved arc extinguisher for facilitating the rupture of arcs drawnbetween the cooperating contacts of the circuit breaker.

Another object of the invention is to provide a circuit breaker havingan improved arc extinguisher structure for facilitating the rupture ofthe are drawn between the separating contacts and a circuit breakerhousing forming a passageway for facilitating the safe expulsion of hotarc gases from the end of the breaker housing opposite to the separatingcontacts.

An additional object of the invention is to provide a small compactcircuit breaker of adequate dielectric strength across the surfaces ofthe breaker housing, without spraying the surfaces with a composition toprevent them from becoming carbonized by the hot arc gases.

A further object of the invention is to provide an improved circuitbreaker of small size capable of safely interrupting overload currentsof large magnitude which is inexpensive in construction and dependablein operation.

The invention, both as to structure and operation, together withadditional objects and advantages thereof, will be best understood fromthe following detailed description of an embodiment thereof, when readin conjunction with the accompanying drawing.

In the drawing:

Figure 1 is a side elevational view with the cover removed of a circuitbreaker embodying the principles of the invention.

Fig. 2 is a vertical sectional view taken on line IIII of Fig. 1 throughthe arc extinguisher.

Fig. 3 is a reduced elevational view of the inside of the cover showingthe recesses and surfaces for receiving and supporting the parts of thecircuit breaker.

Fig. 4 is an exploded perspective view showing the main body of the arcextinguisher, the cover for the arc extinguisher, the plug-in contactmember and the arc runner.

Referring to Fig. l of the drawing, the circuit breaker comprisesgenerally an enclosing casing including a base or housing member 11 anda cover or cooperating housing section 13 (Fig. 3) both made of moldedinsulating material, a stationary contact 15, a movable contact 17, anoperating mechanism 19, a trip device 21 and an arc extinguisher 25.

The stationary contact is rigidly secured to the inner end of aconducting member 22 integral with a plug-in connector member 23supported in the housing 11 and in the cover 13 as will be more fullydescribed later. At the opposite end of the housing 11 is disposed aconducting strip 29 which at its inner end is connected to the tripdevice 21 and which is provided with a terminal connect- Z,?l9,2ll3Patented Sept. 27, 1955 ing means, such as a screw 31, at its outer endfor connecting the breaker in an electric circuit.

The movable contact is rigidly secured on the free end of a U-shapedswitch arm 37 having its legs 57 supported in recesses in the legs 55 ofa U-shaped operating lever of molded insulating material. The operatinglever 35 is pivotally supported by trunnions 36 molded integraltherewith and mounted in suitable companion openings in the housingmember 11 and in the cover 13. An overcenter operating spring 39 isconnected under tension between the bight of the switch member 37 and areleasable carrier 33 pivoted on a pin 41 supported in the housing Illand in the cover 13.

The operating lever 35 is provided with a handle 49 molded integraltherewith and extending outwardly through an opening 51 in the housing11. The operating lever 35 is also provided with an arcuate portion 53cooperating with the housing 11 to substantially close the opening 51 inall positions of the operating lever. The switch member 37 iselectrically connected by a flexible conductor 59 to one end of abimetal element forming part of the trip device 21 which is suitablysecured to and supported by the inner end of the conducting strip 29.

The switch arm 37 is operated to manually open and close the contacts byoperation of the lever 35 which is eflected by manipulation of thehandle 49. Movement of the handle 49 in a clockwise direction carriesthe pivoted ends of the legs 57 of the switch member 37 across to theleft of the line of action of the operating spring 39 which then biasesthe switch member to the open position and causes movement of the switchmembers to the open position with a snap action.

The contacts are manually closed by reverse movement of the operatinglever 35. Counterclockwise movement of the lever 35 from the openposition to the closed position moves the upper pivoted ends of the legsof the switch member 37 across to the right of the line of action of thespring 39 which thus acts to close the contacts with a snap action.

The circuit breaker is tripped open after a time delay in response tooverload currents below a predetermined value and instantaneously inresponse to overload currents above the predetermined value, or inresponse to a short-circuit current, by means of the trip device 21,which will be hereinafter described in detail. Operation of the tripdevice 21 causes release of the carrier 33 whereupon the operatingspring 39 moves the carrier 33 clockwise about its pivot 41. This movesthe line of action of the spring 39 across to the right of the centerline of the switch arm 37 and the spring 39 then acts to move the switcharm to the open position with a snap action. The movement of the carrier33 is arrested by engagement with a projection or wall portion 61 moldedintegral with the housing parts 11 and 13.

The trip device comprises the bimetal element 45 connected by theflexible conductor 59 to the movable switch arm 37 and electromagneticmeans including a magnetic member or armature 63 mounted on the bimetalelement 45 and an H-shaped magnetic member or magnet yoke 65 supportedin a recess 69 in the housing and a companion recess 70 in the cover 13(Fig. 3). The conducting strip 29 is secured to the adjacent end wall ofthe housing 11 by ascrew 71 and the bimetal 45 is rigidly secured bysuitable means such as welding to the upper inner end of the conductingstrip 29 and extends downwardly therefrom.

The magnetic member 63 is rigidly secured to the bimetal element 45 byan enameled rivet 73 which also rigidly fastens a latch member 67 to thebimetal element. The latch member 67 normally engages and releasablyrestrains the carrier 33 in operative position. The latch member 67 isinsulated from the bimetal element 45 and from the armature 63 by thesheets of insulating material (not shown) and by the rivet 733 which isformed from a section of wire precoated with an insulating enamel.

The recesses 69 (Fig. l) and 70 (Fig. 3) in which the legs of the magnetyoke 65 are disposed are provided respectively with shoulders 75 and 77against which the magnet yoke 65 is biased by a light compression spring79 to provide a normal air gap between the magnet yoke 65 and thearmature 63. The spring 79 is compressed between the adjacent end wallof the housing 11 and the magnet yoke 65 and is held in place bycooperating with a spring seat 81 formed on the magnet yoke 65. Thespring seat 81 may be formed by any suitable method such as, forinstance, embossing which also provides a recess 83 on the opposite sideof the magnet yoke 65 which serves as a clearance for the head of therivet '73. The recesses 69 and 70 (Figs. 1 and 3), in which the legs ofthe H-shaped magnet yoke are disposed, are wider at the bottom than theyare at the top to permit pivotal movement of the magnet yoke in thedirection of thermal bending of the bimetal element 45. This arrangementpermits maximum deflection of the bimetal element when it is hot andprevents it from taking a permanent set as it would if its deflectionwere opposed by any substantial forces such as by engaging a fixedmagnet yoke.

Means is provided for calibrating the trip device. This means comprisesa screw 85 threaded through a nut 87 disposed in a recess 89 in theadjacent end wall of the housing 11. The inner end of the screw 85engages the upper end of the conductor strip 29 on which the bimetalelement 45 is mounted. An access opening 91 is provided through whichthe screw may be rotated to adjust the trip device after which theopening 91 may be sealed to prevent tampering. Turning the screw 85causes bending of the conductor 29 and corresponding variation of theposition of the bimetal element according to the direction in which thescrew is rotated to thereby vary the tripping point of the breaker.

Upon the occurrence of a low persistent overload current below apredetermined value of, for instance, ten times normal rated current,the bimetal element 45 is heated and bends toward the right causingrelease of the releasable carrier 33. The releasable carrier 33 causesmovement of the switch member 37 to the open contact position in themanner previously described.

When an overload current above ten times normal rated current or a shortcircuit current occurs, the electromagnetic trip means is energized andthe armature 63 is attracted toward the magnet yoke bending the bimetalelement 45 and causing the latch member 67 to instantaneously releasethe releasable carrier 33 and open the contacts. The specificthermal-magnetic tripping arrangement disclosed herein is being claimedin the copending application Serial No. 285,598, filed May 2, 1952, byL. W. Dyer, now Patent No. 2,677,025, issued April 27, 1954, andassigned to the assignee of this application.

The releasable carrier 33 is reset and relatched and the contacts closedfollowing an automatic operation by first moving the handle 49 clockwiseto the off 'position and then counterclockwise to the on position. Whenthe handle is moved to the off position, the legs 55 of the operatinglever 35 engage a pin in the carrier 33 and move the carriercounterclockwise about its pivot 41. Near the end of this movement, thefree or latching end of the carrier 33 wipes by the latch 67, slightlybending the bimetal element'which then resumes its normal latchingposition.

An important feature of the invention is the novel are extinguisherindicated generally at 25 and the arrangement for venting the hot gasesin substantially a straight line to atmosphere at the end of the housingopposite the separating contacts 1517.

The arc extinguisher consists of a plurality of spaced arc splittingplates 95 of magnetic material shaped as more clearly shown in Figs. 2and 4. Each plate 95 has a slot 97 formed thereon and is provided with aplurality of lugs 99 whereby the plates are rigidly attached at thesides of a U-shaped supporting and insulating housing or enclosure 101composed of a relatively rigid fibrous cellulosic material. The sides ofthe housing 101 are pro vided with openings for receiving the lugs 99which are riveted over to rigidly support the plates in the housing. Theare extinguisher is disposed in the housing and is supported between theprojection 61 on the housing and a corresponding projection 61a (Fig. 3)molded in the cover plate 13, and corresponding surfaces 103 on thehousing and 103a on the cover 13.

A cover 105 (Figs. 1, 2 and 4) of insulating material such as fibre isprovided for the arc extinguisher and has a U-shaped slot therein forreceiving the lower end of the movable switch member 37. The cover 105is held in place by openings 107 therein engaging projections 109 on theupper edges of the housing 101, and by the edges of the cover fittinginto corresponding slots 111 and 113 formed respectively in the breakerhousing 11 and in the cover plate 13. The left-hand end of the arc chutecover 105 has an extension 115 thereon extending upwardly at an anglebetween the conducting member 22 and similar projections 117 and 117a onthe breaker housing and cover respectively, the extension 115 projectinginto a slight recess 119 formed in the under sides of the projections117-117a. The extension 115 and the slots 111 and 113 prevent the cover105 from being blown oil? the arc chute by the pressure of the arcgases, and provide a fairly tight interlocking joint between the arcextinguisher and the casing.

Disposed adjacent the left-hand end of the arc extinguisher is anangular arc runner 121 of magnetic material such as sheet steel havingan upper portion disposed between the upper portion of plug-inconnectors 23 and the conducting member 22 on which the stationarycontact 15 is supported. The lower portion of the arc runner 121 extendsdownwardly at an angle and terminates at a point adjacent the bight ofthe left are plate 95. The are runner 121 is held in place by theengagement of lugs 123 thereon with notches 125 in the side walls of thearc extinguisher housing. It will be noted that the lower end of the arerunner 121 slightly overlaps and rests on the end of an upwardlyextending portion 127 of the insulating bottom portion of the arcextinguisher housing. On low-current breakers the steel arc runner 121may not be needed and the fibre extension 127 will then extend up underthe conductor 22 and close the end of the arc chute in the same manneras the arc runner 121.

The are runner 121 of magnetic material performs several importantfunctions. The magnetic material attracts the end of the are adjacent tothe stationary contact 15 and moves it downwardly into the arc chutewhere the arc and its hot gases come in contact with the U- shapedplates 95. This cools and deionizes the arc and its gases. Without therunner, one end of the arc would remain on the stationary contact 15 andthe plate 95 nearest to this contact would not be very effective. Theare runner also cools the arc terminal as it travels across the surfaceof the runner and eliminates excess burning of the stationary contact.

The wide upper portion of the plug-in connector 23 is supported inrecesses 129 (Fig. 1) and 129a (Fig. 3) respectively in the breakerhousing 11 and in the cover 13. The plug-in connector 23 is formed toprovide a pair of spaced, downwardly projecting blades 131 to permitengagement with a terminal or a bus bar connector (not shown).

A passage 133 for venting the hot gases is formed by the bottom wall 135of the base section or housing 11 and the matching bottom wall 135a ofthe cover section 13, and by matching ribs 137 and 137a formedrespectively on the base section 11 and the cover section 13 which ribsextend to the upperright hand corner of the U are extinguisher to formthe stop 61. The matching ribs 137 and 137a conduct the arc gases underthe thermalmagnetic trip device 21 and prevent the gases from coming incontact with the conducting parts thereof. It will be noted that thebottom portion of the cover 13 overlaps the bottom portion of thehousing 11 as at 139 (Fig. 2) to form a tight seal for preventingleakage of the hot gases through the bottom wall of the breaker housing.

The are splitting plates 95 are slanted at an angle downwardly and awayfrom the separating contacts, and the yoke portion of the right-hand arcplate 95 (Fig. l) is disposed adjacent the throat of the passage 133.The bottom corners of the arc plates 95 are notched to provide clearpassages 141 (Figs. 2 and 4) for the hot gases along the bottom cornersof the arc extinguisher housing to the passage 133 and out through thelatter without obstruction.

It is to be noted that the vent passage 133 extends from the arcextinguisher 25 to the end of the breaker opposite the contacts and thatthe extinguishing plates 95 are slanted at an obtuse angle to the lengthof the passage 133 and toward the end of the breaker at which thepassage vents the arc gases to atmosphere. The outer end 143 of the ventpassage is slanted upwardly, being provided with a rib 145 having aninclined approach face to direct the gases above the metal mountingbracket 147 which may be at ground potential. This helps to avoid anypossibility of flash-over from line to ground through the vent passage.

When the contacts separate, the are drawn therebetween moves down thearc runner 121 to the adjacent are splitter plate 95 and is then brokenup between the arc plates and extinguished. The heat due to the arccauses an expansion of the air in the circuit breaker which blows thehot gases downward through the spacers between the plates 95, along thepassages 141 and out through the passage 133. The legs of the U-shapedcover 195 or" the arc extinguisher extend inwardly (Fig. 2) far enoughto cause a turbulence of the hot gases which might flow upwardly andsubstantially prevents the hot gases from moving out of the arcextinguisher housing into the space around the breaker operatingmechanism. This action is aided by the fact that the plates 95 areslanted toward the vent passage 133 and are notched at the corners toprovide the passages 141, thus making it easy for the gas pressure to bereleased without blowing up into the mechanism of the breaker. The coverplate 105 fits into the grooves 111 and 113 in the base and coverrespectively, and acts as a barrier between the contact and terminal 23,which are at line potential, and the metal parts of the mechanism whichare at the potential of the load terminal. There is then no direct pathacross the surfaces of the molded phenolic insulating material of thehousing sections 11 and 13 between parts at opposite potentials.

With the construction described it has been made possible to eliminatethe step of spraying the inside of the housing sections 11 and 13adjacent the arc extinguisher with a coating of a composition to protectthe molded material from being carbonized by are gases and providing asurface of low dielectric strength which could cause flash-over betweenthe contact on the line terminal 23 and the mechanism parts at thepotential of the load terminal 31. However, if increased dielectricstrength is desired, the spraying may be used.

Having described the invention specifically in accordance with thestatutes, it is to be understood that various changes and modificationscan be made without departing from the spirit of the invention.

We claim as our invention:

1. A circuit interrupter including an enclosing casing of moldedinsulating material and separable contact means disposed adjacent oneend wall of said casing for establishing an are, are extinguishing meansfor extinguishing the arc comprising a plurality of spaced slottedplates slanted away from said separable contact means, an insulatinghousing supporting said plates, a metallic arc runner disposed in saidhousing adjacent said contact means and terminating proximate to theadjacent one of said plates at one end of said housing for drawing thearc to said plates, and portions of said casing molded integraltherewith forming a passageway extending from the other end of said areextinguisher housing to the end of said casing opposite said contactmeans for venting the gases of the arc.

2. A circuit interrupter including a casing of molded insulatingmaterial for enclosing said interrupter, contact means comprisingstationary and movable contacts for drawing an arc, arc extinguishingmeans for extinguishing the arc comprising a plurality of spaced slottedplates, a U-shaped insulating housing for supporting and enclosing saidplates, a terminal connector supported in said casing and having aconductor extending into one end of said are extinguisher housing forsupporting said stationary contact, a projection on said casing adjacentsaid conductor, a cover on said are extinguisher housing having aportion extending under said projection into the space between saidconductor and said projection, said cover having openings therein forreceiving projections on said housing to hold said cover in place, awall molded integral with said casing and terminating adjacent the otherend of said arc extinguisher housing, said wall cooperating with otherportions also molded integral with said casing to form a passagewayextending from said are extinguisher for venting the gases of the areout of said casing at the end thereof opposite said contact means.

3. A circuit interrupter including a casing of molded insulatingmaterial for enclosing said interrupter, contact means comprisingstationary and movable contacts for drawing an are, are extinguishingmeans for extinguishing the are comprising a plurality of spaced slottedplates, a U-shaped insulating housing for supporting and enclosing saidplates, a terminal connector supported in said casing and having aconductor extending into one end of said are extinguisher housing forsupporting said stationary contact, an arc runner supported on saidhousing and having one end disposed adjacent said conductor and theother end disposed proximate to the adjacent slotted plate of said areextinguisher, a projection on said casing adjacent said conductor, acover on said arc extinguisher housing having a slot therein forreceiving said movable contact and having a portion extending betweensaid conductor and said projection, a wall molded integral with saidcasing and terminating adjacent the other end of said are extinguisherhousing, said wall cooperating with other portions also molded integralwith said casing to form a passageway extending from said areextinguisher for venting the gases of the are out of said casing at theend thereof opposite said contact means.

4. A circuit interrupter having an enclosing casing formed of two piecesof molded insulating material, stationary and movable contacts forestablishing an are, an arc extinguisher structure for extinguishing thearc comprising a plurality of spaced slotted plates, a U-shapedinsulating housing for supporting said plates, a terminal supported insaid casing and having a conducting portion extending into one end ofsaid are extinguisher for supporting said stationary contact within saidhousing, a cover of insulating material for said are extinguisherhousing, each piece of said casing having a recess therein for receivingone of the opposite edges of said cover, means molded integral with saidcasing pieces forming a passageway extending to the opposite end of saidcasing from said terminal for venting the gases of the are, saidpassageway having an enlarged portion disposed adjacent the opposite endof said are extinguisher housing from said contacts and into which oneend of the arc extinguisher extends.

5. A circuit interrupter including an open-sided casing of moldedinsulating material and a closure member also of molded insulatingmaterial mounted on the open side of said casing, stationary and movablecontacts disposed adjacent one end wall of said casing for establishingan are, an arc extinguisher comprising a plurality of spaced slantedplates, an insulating housing for supporting said spaced plates, aterminal member of conducting material supported at one end of saidcasing and having a portion extending into one end of said areextinguisher housing for supporting said stationary contact, and saidopensided casing and said closure member having portions molded integraltherewith cooperating to form a passageway from the other end of saidare extinguisher housing to the end of said casing opposite saidterminal to vent the gases heated by the arc, and said slanted platesbeing slanted away from said contacts and toward said passageway.

6. A circuit interrupter including an open-sided casing of moldedinsulating material and a closure member also of insulating materialmounted on the open side of said a casing, stationary and movablecontacts for establishing an are, an arc extinguisher comprising aplurality of spaced plates, an insulating housing for supporting saidspaced plates, a terminal member of conducting material supported at oneend of said casing and having a portion extending into one end of saidare extinguisher housing for supporting said stationary contact withinsaid housing, said open-sided casing having portions molded integraltherewith to form a passageway from the other end of said areextinguisher housing to the end of said casing opposite said terminal tovent the gases heated by the arc, and said spaced plates being slantedtoward said passageway to direct the gases thereinto and out said end ofthe casing.

7. A circuit interrupter including an open-sided casing of moldedinsulating material and a closure member also of insulating materialmounted on the open side of said casing, stationary and movable contactsfor establishing an are, an arc extinguisher comprising a plurality ofspaced parallel plates, an insulating housing for supporting said spacedplates, a terminal member of conducting material supported at one end ofsaid casing and having a portion extending into one end of said areextinguisher housing for supporting said stationary contact, saidopen-sided casing having portions molded integral therewith to form apassageway from the other end of said are extinguisher housing to theend of said casing opposite said terminal to vent the gases heated bythe arc, and said spaced plates being slanted toward said passageway andhaving spaces between the ends of the slotted plates and the insulatinghousing supporting them to provide a continuous passage from the spacesbetween the plates to said passageway to direct the gases thereinto andout said end of the casing.

8. A circuit interrupter including an open-sided casing of moldedinsulating material and a closure member also of molded insulatingmaterial mounted on the open side of said casing, stationary and movablecontacts for establishing an are, an arc extinguisher comprising aplurality of spaced plates, an insulating housing for supporting saidspaced plates, a terminal member of conducting material supported at oneend of said casing and having a portion extending to one end of said areextinguisher housing for supporting said stationary contact within saidhousing, a metallic arc runner disposed in said are extinguisher housingadjacent said stationary contact and terminating proximate to theadjacent arc plate, and said open-sided casing and said closure memberhaving portions molded integral therewith cooperating to form apassageway from the other end of said are extinguisher housing to theend of said casing opposite said terminal to vent the are gases, saidportions of said casing and closure member cooperating with said arcextinguisher housing to hold said housing in place.

"9. A circuit interrupter including an open-sided casing of moldedinsulating material and a closure member also of molded insulatingmaterial mounted on the open side of said casing, stationary and movablecontacts for establishing an are, an arc extinguisher comprising aplurality of spaced slotted plates of magnetic material, an insulatinghousing for supporting said spaced plates adjacent the path of openingmovement of said movable contact, a terminal member of conductingmaterial having a formed-over portion extending into an end of said areextinguisher housing for supporting said stationary contact, portionsmolded integral with said casing and said closure member forming aninwardly extending projection disposed adjacent the formed over portionof said terminal, a cover for said are extinguisher housing having aportion extending under said projection, portions molded integral withsaid open-sided casing and said closure member together forming apassageway extending from the other end of said are extinguisher housingto the end of said casing opposite said contacts for venting the gasesof the arc, and said other end of said are extinguishing housingextending into the adjacent end of said passageway.

10. A circuit interrupter including an enclosing casing of moldedinsulating material, terminals at opposite ends of said casing,stationary and movable contact means disposed adjacent one end wall or"said casing for drawing an arc generally along the bottom of saidcasing, arc extinguishing means for extinguishing the are comprising aplurality of spaced slotted plates, an insulating housing supportingsaid plates, means for said casing defining a vent at the end of saidcasing opposite said stationary contact for venting the gases of thearc, and said spaced plates being slanted toward said vent to direct thegases thereinto and out said end of said casing.

11. A circuit interrupter including an enclosing casing of moldedinsulating material, terminals at opposite ends of said casing,stationary and movable contacts disposed adjacent one end wall of saidcasing for drawing an are generally along the bottom of said casing, anarc extinguisher comprising a plurality of spaced plates, an insulatinghousing for supporting said plates, means defining a vent passage at theend of said casing opposite said stationary contact, each of said spacedplates having notches at the corners thereof, said notches cooperatingwith said housing to form continuous passages extending along the bottomof said are extinguishing housing and into said vent passage leading tothe end of said casing opposite said stationary contact, said spacedplates being slanted toward said vent passage to direct the gasesthereinto and out said end of said casing.

12, A circuit interrupter having an enclosing casing formed of two partsof insulating material, terminals at opposite ends of said casing,stationary and movable contacts disposed adjacent one end Wall of saidcasing for drawing an are generally along the bottom of said casing, anarc extinguisher comprising a plurality of spaced slotted plates, aninsulating housing for supporting said spaced plates, a cover for saidhousing, each of the two pieces of said casing receiving one of theopposite edges of said cover, means on said pieces of said casingforming a vent passage at the end of said casing opposite saidstationary contact, said means on said pieces of said casing cooperatingwith said are extinguisher housing to hold it in place, and said spacedplates being slanted toward said vent passage to direct the gasesthereinto and out of said end of said casing.

13. A circuit interrupter including an enclosing casing formed of twopieces of insulating material, terminals at opposite ends of saidcasing, stationary and movable contacts at one end of said casing fordrawing an are generally along the bottom of said casing, an arcextinguisher comprising a plurality of spaced slotted plates, aninsulating housing for supporting said plates, means defining a ventpassage at the end of said casing opposite to said stationary contact, acover for said are extinguisher housing, each of the two pieces of saidcasing receiving one of the opposite edges of said cover, each of saidspaced plates having notches at the corners thereof cooperating withsaid housing to form continuous passages extending along the bottom ofsaid casing and into said vent passage leading to the end of said casingopposite said stationary contact, and said spaced plates being slantedtoward said vent passage to direct the arc gases thereinto and out saidend of said casing.

References Cited in the file of this patent UNITED STATES PATENTS VonHoorn Dec. 22, 1936 Graves, Jr June 3, 1941 Bingenheimer et a1 May 8,1951 Thomas Feb. 3, 1953

